"Wild Wild West" was a Warner Bros. picture. As I recall, they had the Strasburg shops overhaul the "Mason," the main work being new boiler tubes (one of the Strasburg guys could probably fill in more than that). They also built a parlor car and baggage/"laboratory" car on the frames of old refrigerator cars; both are now at the Fillmore & Western.
"God and Generals" built a faux station and water tower on the tracks just behind the B&O Museum, meaning the "Mason" barely had to get out of bed to appear in that film. Makes me wonder why they didn't just do that for "Cold Mountain," rather than trying to send "Eureka" on a 5,000 mile round trip.